Johnny, ORP is a strange beast.
You were very fortunate to have an orp of 400 without running ozone. And I'm not sure this means anything in the health of your tank.
Many things affect ORP and I would not rely on ORP to tell you the health of your tank. It can be very misleading to aquarists.
I've been dabbling with ORP and ozone for a few years now and there is no rhyme or reason to the numbers. Period.
I use an ORP meter to monitor my ozone injection.
If you are not using ozone, my recommendation would be to put your ORP meter in the drawer or sell it to someone who needs it.
You don't.
If you are seeing some distress in your corals, I would look to another reason.